31 CFR § 211.1 - Withholding delivery of checks.
(a) It is hereby determined that postal, transportation or banking facilities in general or local conditions in the Republic of Cuba and the Democratic People's Republic of Korea (North Korea) are such that there is not a reasonable assurance that a payee in those areas will actually receive checks or warrants drawn against funds of the United States, or agencies or instrumentalities thereof, and be able to negotiate the same for full value.
(b) A check or warrant intended for delivery in any of the areas named in paragraph (a) of this section shall be withheld unless the check or warrant is specifically released by the Secretary of the Treasury.
(c) Before a check or warrant drawn against funds blocked pursuant to the provisions of Executive Order No. 8389 (3 CFR, 1943 Cum. Supp.), as amended, and which remain blocked under the proviso clause of General License No. 101 of the Foreign Funds Control Regulations (31 CFR 520.101) may be released, it will be necessary for a license authorizing the release to be issued by the Department of the Treasury, Office of Foreign Assets Control, pursuant to E.O. 8389, as amended. In this regard, attention is also directed to the following regulations issued by the Secretary of the Treasury:
(1) The Foreign Assets Control Regulations issued on December 17, 1950 (31 CFR part 500), pursuant to Executive Order 9193 (3 CFR, 1943 Cum. Supp.), which prohibit transactions involving payments to nationals of the Democratic People's Republic of Korea (North Korea), the Socialist Republic of Vietnam, and Democratic Kampuchea, except to the extent that any such payments have been authorized by appropriate license,
(2) The Cuban Assets Control Regulations issued on July 8, 1963 (31 CFR part 515), pursuant to the same authority, which prohibit similar transactions with nationals of Cuba unless licensed, and
(3) The Iranian Assets Control Regulations issued on November 14, 1979 (31 CFR part 535), as amended on April 17, 1980, pursuant to Executive Orders 12170 and 12211, which prohibit transactions in property of the Iranian Government or its instrumentalities and transfers of funds to persons in Iran, except as authorized by appropriate license.
(d) Powers of attorney for the receipt or collection of checks or warrants or for the proceeds of checks or warrants included within the determination of the Secretary of the Treasury set forth in paragraph (a) of this section will not be recognized.